Celiac disease is activated by dietary exposure to proteins in wheat, rye, barley and oats. The gliadin fraction of gluten in wheat and similar proteins in the other grains activate disease. Moreover, the complete amino acid sequence of A-gliadin, a major alpha gliadin component known to activate celiac disease, is known. Nonetheless, the specific peptide(s) within A-gliadin and other grain proteins that activate disease are net known. We hypothesize that celiac disease is activated by a specific peptide present in the A-gliadin molecule and that the peptide, and the amino acid residues in the peptide that are required for disease activation, can be unambiguously defined. The overall goal of these studies is to define the minimal amino acid sequence in A-gliadin that is required to activate celiac disease, determine the specific amino acids within that peptide motif that are critical for disease activation, and test whether analogs of the disease-activating peptide can specifically block disease activation. In Aim 1, a series of overlapping peptides will be used to detect the putative peptide(s) in A-gliadin that activate disease. These studies will use a rapid and simple new in vitro readout system developed in our laboratory for systematic screening of a large number of peptides for putative disease-activating properties. In Aim 2, the relevance of those peptide(s) to in vivo disease activation will be tested, using a modification of the recently described rectal gluten challenge test. In this regard, gliadin activates changes in the rectal and colonic mucosa of celiac disease patients, but not normal individuals, whereas control proteins do not. In Aim 3, the peptide(s) that test positive in Aims l and 2 will be further studied by testing their ability to activate small intestinal damage in vivo, using peptide perfusion of an isolated intestinal segment. In Aim 4, the minimum length of the A- gliadin peptide required for activation of celiac disease will be determined using truncation analysis. Subsequently, specific conservative and non-conservative amino acid replacements will be used to determine the critical disease-activating residues. Finally, peptide analogs which are related to the disease-activating peptide, but which do not directly activate disease themselves, will be tested for their ability to block activation of celiac disease using the in vitro and in vivo assay systems. The information gained from these studies may lead to new therapeutic modalities to prevent and treat celiac disease and will allow specific models of disease pathogenesis to be directly tested.